Martian Sand Dunes Are Slowpokes

This Mars Global Surveyor image shows a martian crater that has been encroached by a field of dark, wind-blown sand dunes in the Syrtis Major volcanic region of the red planet.Credit: NASA/JPL/Malin Space Science Systems.

The sand dunes of Mars are in no rush to move across
the red planet?s surface, new research shows.

It can take up to 1,000 years for dunes to move
just a few meters on Mars, largely due to the planet?s apparent lack of moving
surface water, weak winds and thin atmosphere, said the study?s author Eric Parteli.

?Mars dunes move much slower than Earth?s
dunes,? said Parteli, a researcher at the University if Stuttgart in Germany, in an e-mail interview.

Parteli and colleague Hans Hermann, of Brazil's Federal University of Ceará, used computer simulations to reproduce actual Martian dunes observed by the Mars Orbiter Camera aboard NASA's Mars Global Surveyor spacecraft. The images were taken before Mars
Global Surveyor went silent last year, ending its 10-year study
of the red planet?s surface.

The scientists found that a small Martian sand
dune about 3-feet (1-meter) tall would need wind speeds 75 mph (120 kph) to
move appreciably.

Since such winds are extremely rare on the red
planet, occurring just a few times each decade, the dunes of Mars are confined to
their glacial pace, the researchers said. The research is detailed in the
recent edition of the journal Physical Review E.

The limiting factor, Parteli said, is the
Martian atmosphere.

On Earth, sand dunes are shaped by water and
wind. But extensive scans of Mars by NASA's
Spirit and Opportunity rovers and orbiting spacecraft have yet to find
liquid water on the red planet's surface.

Dunes on Mars can reach
heights of 20 feet (6 meters) and come in shapes ranging from crescents to
stars, though similar sand dune formations are seen on Earth. The difference, Parteli
said, is that Mars tends to span more crescent-shaped (barchan) and transverse
dunes, while the long, sinewy linear dunes are more common on Earth.

And while Martian winds can kick up sky-blotting
dust storms like those that plagued the Spirit and Opportunity rovers this
summer, the atmosphere of Mars is 100 times less dense than that of Earth. The
result, researchers said, are weaker winds that only rarely reach strengths
capable of moving Martian dunes.

?If sand-moving winds on Mars occurred as
frequently as they occur on Earth, Mars dunes would move 10 times faster than
Earth?s dunes,? Parteli told SPACE.com.

According to the simulations, winds strong
enough to create bimodal dunes - sand structures shaped by winds blowing in
perpendicular directions - could take about 50,000 years to complete their
work.

"Of course, there are many winds on Mars
which change direction in a scale of hours," Parteli said. "But
they're just not strong enough to move sand."